Drop optional context parameters

[liufengyun]

Drop optional context parameters

Note: This is a breaking change, a JIP is deserved to justify.

Summary

Il semble que la perfection soit atteinte non quand il n'y a plus rien à ajouter, mais quand il n'y a plus rien à retrancher.

Perfection, it seems, is attained not when there is nothing more to add, but when there is nothing more to take away.

— Antoine de Saint-Exupéry, Terre des Hommes (1939)

This proposal drops optional context parameters — the form in which a declaration carries a default:

param pageWidth: Int = 80   // dropped

Such a default is supplied automatically wherever no binding is in scope. After this change a declaration states only a requirement, and a caller provides the value:

param pageWidth: Int
with pageWidth = 80 in render(document)

Nothing else about context parameters changes: with, receives, allow, shadowing, and capture keep their current meaning.

param states a requirement, receives tracks it, allow bounds it, and with provides it.

See more in the JIP.

Checklist

• Added / updated tests under tests/pos/ or tests/warn/
• Docs updated if the change affects user-visible behavior
• All commits are signed off (why?)

How to sign off commits

Use git commit -s to add the Signed-off-by line automatically:

To add a sign-off to the last commit retroactively:

git commit --amend -s --no-edit

To add sign-off to the last 3 commits:

git rebase --signoff HEAD~3

Security impact

No

Compatibility impact

This is a breaking change.

• Source compatibility: existing code continue to compile
• SAST compatibility
  • forward compatibility: new libraries can be used by old compiler
  • backward comopatibility: old libraries can be used by new compiler
• Standard Library compatibility:
  • forward compatibility: new code can work with old stdlib
  • backward compatibility: old code work with the new stdlib
• Runtime Library compatibility:
  • forward compatibility: new code can work with old runtime
  • backward compatibility: old code work with the new runtime
• Build tool
  • Build spec compatibility: old projects continue to build
  • Joy package compatibility: old .joy can be consumed by new build tool

---